Method and apparatus for mold clamping in an injection molding machine and the like

ABSTRACT

Method for mold clamping of the present invention is capable of shortening a molding cycle without any initial setting works for an engaging position of a tie bars. The method is constituted the steps of moving the tie bars in the direction of mold closing during mold close operation, judging a relative moving speed between a movable die plate and the tie bar to be within a predetermined value, engaging the tie bars with the movable die plate mechanically by operating an engaging means when the relative moving speed is judged to be within the value, then further moving the movable die plate against a fixed die plate under engagement, and after contact of a movable mold with a fixed mold driving a mold clamping cylinder, thereby executing mold clamping operation.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and apparatus for moldclamping in an injection molding machine and the like such as plasticinjection molding machine or die casting machine, specifically to thatfor mold clamping to combine a movable die plate with tie barsmechanically during mold close operation of the movable die plate so asto shorten a molding cycle.

[0003] 2. Description of Related Art

[0004] There are disclosed in Japanese laid open patent numbers10-296809 and 10-296810, methods for mold clamping to combine themovable die plate with the tie bars mechanically during the mold closeoperation of the movable die plate so as to shorten the molding cycle.

[0005] In the former (10-296809), as shown in FIGS. 4 and 5 (not shownhere) of it, there is slidably arranged a movable die plate on tie barswhich one ends are fastened to a fixed die plate. The movable die plateis provided with a clamping cylinder near a slide portion with the tiebars, and a piston member of the cylinder protrudes from the movable dieplate.

[0006] In the movable die plate, there is provided with an open andclose mechanism mounting nuts formed with multi-split or dividedportions called as half nuts, which engage with a screw portion formedat circumference of the tie bars. The nuts engage with the screw portionby driving the open and close mechanism when the movable die platereaches a position just before a mold close position.

[0007] In the former it is disclosed that engagement of the screwportion with the nuts are possible by arranging plural pairs of halfnuts even under movement of the movable die plate.

[0008] In the latter (10-296810), as shown in FIG. 1 (not shown here) ofit, there is arranged a movable die plate providing with a ram cylinderfor mold clamping therein and a pair of half nuts on both sides of themovable die plate through which tie bars passe, one end of the tie barsbeing fastened to a fixed die plate. The one half nuts near the fixeddie plate can move in the direction of the tie bars axes independently.At initial setting an appropriate position is defined for engaging withthe tie bars. At each molding cycle operation, the other half nutsengages with the tie bars by driving it after the movable die platecontacts the one half nuts at its end surface during the mold closeoperation. In the case, the distance between both the half nuts isformed to keep at the value of integral multiple to the screw pitch ofthe tie bars. In the cases mentioned above, the tie bars are fastened tothe fixed die plate.

[0009] Another arrangement for moving tie bars themselves during themold close operation is proposed in Japanese laid open patent number10-296739 wherein an engaging mechanism operates while both a movabledie plate and the tie bars move. Such an arrangement for moving the tiebars themselves are explained, referring to FIGS. 6 to 9 attached.

[0010] In FIGS. 6 to 9 a reference numeral 10 represents a fixed dieplate. The fixed die plate 10 provides with a fixed mold 12. A movabledie plate 18 providing with a movable mold 16 is disposed against thefixed die plate 10 and is capable of advancing and retracting thereto.

[0011] A nut member 24 is mounted on the under portion of the movabledie plate 18. The nut member 24 is screwed with a screw member 22coupled through a coupling member 22 a to a servomotor 20 for the moldopen and close operation, which is fastened to the fixed die plate 10 asa driving means.

[0012] Rotating of the screw member 22 causes the movable die plate 18to advance or retract to the fixed die plate 10, thereby executing themold open and close operation of the movable mold 16 to the fixed mold12.

[0013] Furthermore, half nuts 28 for mold clamping as one of an engagingmeans are mounted on the left side of the movable die plate 18 throughwhich tie bars 14 are disposed. The tie bars 14 have a screw or grooveportion 14 a at its one end portion as the other engaging means, towhich the half nuts advance and engage by means of a cylinder 26.

[0014] Also, die clamping cylinders 30 are mounted on the fixed dieplate 10 at its coupling portion with the tie bars 14. A piston 14 bformed at the other end portion of the tie bars 14 are slidably insertedin the cylinders 30.

[0015] Accordingly, the tie bars 14 are capable of advancing orretracting in the direction of its axis.

[0016] Furthermore, as shown in FIG. 8, there is mounted a servomotor 32on the out side of the cylinders 30. The servomotor 32 is coupledthrough a coupling member 31 a to a screw member 31 screwed into a rodportion 14 c of the tie bars 14 at the piston 14 b. Accordingly, the tiebars 14 are moved in the direction of the axis by rotating theservomotors 32. Besides, in FIG. 6, a numeral 34 represents a nozzleportion of the injection molding machine.

[0017] In such a complex mold clamping apparatus as illustrated in FIGS.6 to 9, when works are executed for mounting mold 12 and 16 on the fixeddie plate 10 and the movable die plate 18, and for adjusting a distancebetween them, the engagement between the tie bars 14 and the movable dieplate 18 is released by the half nuts 28 to allow the mold closeoperation starting from a most retracted or opened position.

[0018] Then, the servomotor 20 executes the mold close operation. In thecase, the half nuts 28 is closed at the most advanced or closed positionby operating the cylinders 26.

[0019] Usually, it is difficult to appropriately engage the half nuts 28with the screw portion 14a, because of a phase shift between a screwthread and a screw core of thread in both the half nuts 28 and the screwportion 14 a.

[0020] To avoid the effect of such a phase shift, the servomotors 32 formoving the tie bars 14 drive it with micro motion, and the servomotors32 stops to move it at a position that the half nuts 28 and the screwportion 14 a are capable of engaging. Then, as shown in FIG. 7, the halfnuts 28 comes into appropriate engagement with the screw portion 14 a. Aposition detector (not shown) detects the position of the tie bars 14corresponding to the appropriate engagement, and the detected value isstored in a memory of a controller (not shown).

[0021] Accordingly, in the molding operation after setting theappropriate position, the servomotors 32 controls movement of the tiebars 14 so that the movable die plate 18 always locates at the mostadvanced position. Thus, the adjusting work finishes by determining thedistance between the fixed die plate 10 and the movable die plate 18when the movable mold 16 contacts with the fixed mold die 12 in the dieclose operation.

[0022] According to the complex mold clamping apparatus as mentionedabove, the movable die plate 18 shown in FIG. 6 advances by driving theservomotor 20 after adjusting the engaging position of the half nuts 28for mold clamping. When the movable die plate 18 reaches a position “B”in FIG. 9 near the most advanced position, the tie bars 14 starts tomove in the direction of right in FIG. 9 by driving the servomotors 32,then the servomotors 20 and 32 are controlled so as to synchronize inthe relative moving speed between the movable die plate 18 and the tiebars 14, namely so as to become zero in the relative moving speed.

[0023] When the relative moving speed between the movable die plate 18and the tie bars 14 synchronizes at the position “A” in FIG. 9 and thenit becomes zero at a specific position, the half nuts 28 operates toclose, thereby engaging with the screw portion 14 a of the tie bars 14as shown in FIG. 9.

[0024] Also, according to the complex mold clamping apparatus, asmentioned above, molding operation including the mold close operationillustrated in FIG. 9 starts after adjusting the position of the halfnuts 28 to engage with the screw portion 14 a.

[0025] In the molding operation, first, the movable die plate 18 shownin FIG. 6 advances by driving the servomotor 20. When the movable dieplate 18 reaches a position “B” in FIG. 9 near the most advanced moldclose position, the tie bars 14, which already moved in the left fromthe position stored in the memory, starts to move in the direction ofright in FIG. 9 by driving the servomotors 32, then the servomotors 20and 32 are controlled so as to synchronize in the relative moving speedbetween the movable die plate 18 and the tie bars 14, namely so as tobecome zero in the relative speed, the relative moving speed beingprocessed in the controller.

[0026] Then, an engagement between the half nuts 28 and the screwportion 14 a is detected at the position “A” when the relative movingspeed in the direction of right between the movable die plate 18 and thetie bars 14 is synchronized. In case that the half nuts 28 is at aposition appropriate for the engagement the half nuts 28 is operated toclose and engage with the screw portion 14 a, holding the relativemoving speed to be zero by the controller.

[0027] When the engagement is completed and the movable die plate 18reaches the most advanced or close position, the position detectordetects a position of the tie bars 14. The detected value is comparedwith that stored in the memory as the position of the tie bars 14 whenadjusting the distance between the movable die plate 18 and the fixeddie plate 10. In case of coincidence between the values, the moldclamping and boosting operation starts.

[0028] On the other hand, in case of inappropriate position forengagement, the speed of either one of servomotors 20 or 32 is adjusted.In FIG. 9, the servomotors 32 for slidably moving the tie bars 14 arecontrolled variably in speed as shown in dotted lines. When the tie bars14 reach an appropriate position “C” in FIG. 9 for engagement, the speedof the tie bars 14 returns to the relative moving speed insynchronization as before. Then, as stated, the half nuts 28 areoperated to close and engage with the screw portion 14a, holding therelative moving speed to be zero by the controller.

[0029] In this case, without appropriately positioning for engagement,it is also possible to smoothly close the half nuts 28 in such a waythat the half nut 28 is provided with wider spiral or square grooves,which engage with the screw portion 14 a of the tie bars 14, so as toform the groove with space enough to enter a corresponding screw threadof the screw portion 14 a therein.

[0030] Second, hydraulic pressured oil is introduced into a chamber 30 afor mold clamping operation formed in the die clamping cylinders 30,which generates high clamping force through the tie bars 14. After that,successive processes of injecting melt resin material into a moldthrough the nozzle 34 of the injection molding machine, filling andcooling are executed to produce molded articles. Then, a die openingprocess starts.

[0031] In the mold opening process, hydraulic pressured oil isintroduced into a chamber 30 b for return (mold opening in highpressure) formed in the mold clamping cylinders 30. Driving theservomotor 20 in reverse can do the mold opening operation, because themovable die plate 18 is screwed through a nut member 24 with a feedscrew member 22. Furthermore, the engagement between the half nuts 28and the tie bars 14 are released during the mold opening operation, andat the same time driving the servomotors 32 in reverse allows the tiebars 14 to move at the position “B” of FIG. 9 in the direction of left.Thus, one whole cycle of injection molding terminates.

[0032] Accordingly, in the complex mold clamping apparatus illustratedin FIGS. 6 to 9 it is possible to shorten the cycle time of oneinjection molding, because the half nuts 28 can open and close duringthe mold open and close operation.

[0033] In the above, three prior arts disclosed in Japanese laid openpatents are illustrated. However, in case of initial setting, namelyexchanging the mold to new one, it is necessary for any one of the priorarts to arrange the half nuts so as to be in engagement with the screwportion formed on the tie bars at the specific position, and further tomemorize and hold the position mechanically or electrically.

[0034] In Japanese laid open patent number 10-296809, the engaging meansmoves together with the movable die plate to the tie bars, and executesengagement operation while moving. In the case, there is a disadvantagethat it takes time because finally the speed of the movable die platemust be set slower, though a plurality of half nuts is provided tosuppress a shock at the engagement.

[0035] In Japanese laid open patent number 10-296810, a pair of halfnuts for mold clamping must be arranged on both side of the movable dieplate, respectively.

[0036] Therefore, there is a disadvantage in this case that, in additionto a structural complexity another drive means is required toindependently drive the half nut located at the one side of the movabledie plate.

[0037] Furthermore, in the case explained above referring to FIGS. 6 to9, it is disclosed that while the movable die plate 18 moves, therelative moving speed between the half nuts 28 and the tie bars 18 arecontrolled and held to become zero, and the half nuts 28 executesengagement operation under the relative moving speed “zero”. There isalso a disadvantage in the case that drive control for both of themovable die plate and the tie bars are complex because the relativeposition between the half nuts 28 and the tie bars 18 must be adjustedat an appropriate position for engagement while both of them move.

[0038] As shown in FIG. 8, the servomotors 32 are mounted on the endportion of the mold clamping cylinders 30 to slidably move the tie bars.There is also another disadvantage in this case that two different drivemeans (mold clamping cylinders 30 and servomotors 32) are required formoving the tie bars at two different timings, one of which is for themold close operation in the direction of axis of the tie bars 14 and theother is for the mold clamping operation.

[0039] The inventors of the preset invention have investigateddiligently concerning such disadvantages in the prior arts, and as theresult, convinced that such disadvantages could be solved by utilizingthe relative speed and controlling a timing for driving the engagingmeans rather than controlling and holding the relative speed to be zero.

SUMMARY OF THE INVENTION

[0040] Accordingly, an object of the present invention is to provide anew method and apparatus for mold clamping capable of engaging withoutany initial setting works for defining an engaging position on a tiebars in an injection molding machine and the like.

[0041] To achieve the object, the present invention provides a methodfor mold clamping in an injection molding machine and the like having amold clamping mechanism comprising a fixed die plate fixedly mounting afixed mold thereon, a movable die plate fixedly mounting a movable moldthereon and facing to the fixed die plate, a tie bars supported at oneend portion by the fixed die plate and slidably supporting the movabledie plate so as to advance and retract to the fixed die plate, a firstdrive means for executing mold open and close operations by advancingand retracting the movable die plate to the fixed die plate, a seconddrive means for executing mold clamping operation by pressing themovable die plate against the fixed die plate after the movable moldcontacts with the fixed mold by operating the first drive means, a thirddrive means for executing relative movement between the tie bars and themovable die plate in the direction of the tie bars axis, and an engagingmeans mounted on the movable die plate for executing an engagement withan engaging portion formed on circumference of the tie bars, the methodcomprising the steps of starting movement of the tie bars in thedirection of mold closing by the third drive means so that the tie barsmoves at different moving speed with that of the movable die plateduring mold close operation in which the movable die plate moves againstthe fixed die plate by the first drive means, judging a relative movingspeed between the movable die plate and the tie bars within apredetermined value, engaging the tie bars with the movable die platemechanically by operating the engaging means when the relative movingspeed is judged to be within the value, then driving the second drivemeans, thereby executing mold clamping operation.

[0042] Furthermore, to achieve the object, the present inventionprovides an apparatus for mold clamping in an injection molding machineand the like having a mold clamping mechanism comprising a fixed dieplate fixedly mounting a fixed mold thereon, a movable die plate fixedlymounting a movable mold thereon and facing to the fixed die plate, a tiebars supported at one end portion by the fixed die plate and slidablysupporting the movable die plate so as to advance and retract to thefixed die plate, a first drive means for executing mold open and closeoperations by advancing and retracting the movable die plate to thefixed die plate, a second drive means for executing mold clampingoperation by pressing the movable die plate against the fixed die plateafter the movable mold contacts with the fixed mold by operating thefirst drive means, a third drive means for executing relative movementbetween the tie bars and the movable die plate in the direction of axesof the tie bar and an engaging means mounted on the movable die platefor executing an engagement with an engaging portion formed oncircumference of the tie bars, and further having a mold clampingcontroller for drive control of the first drive means, the second drivemeans, the third drive means and the engaging means,

[0043] the mold clamping controller constituting

[0044] a first command division for instructing a low moving speed ofthe movable die plate to the first drive means during mold closeoperation, and for instructing a moving speed of the tie bars differentfrom the low moving speed to the third drive means at the same time whenthe low moving speed is instructed or thereafter,

[0045] a detector for detecting a relative moving speed between themovable die plate and the tie bars,

[0046] a setting division for setting a preferable relative movingspeed, within which the engaging means is capable of engagement, and

[0047] a second command division for instructing the engaging operationwhen an output signal of the detector reaches the preferable relativemoving speed.

[0048] In the case, the second drive means can be constituted to usealso as the third drive means.

[0049] Further, in the case, the second drive means and the third drivemeans can be constituted to provide with a mold clamping cylinderslocated in the movable die plate, and the third drive means can beconstituted to provide with a screw portion formed on circumference ofthe tie bars which locate at a supporting portion in the fixed dieplate, nuts located in the fixed die plate, which is screwed with thescrew portion and refrained from moving in the axis direction thereofand a drive motor for rotating the nut.

[0050] The apparatus constituted as stated in the above executes a moldclamping operation in such away that, while the mold close operation inwhich the first drive means moves the movable die plate to the fixed dieplate, the third drive means moves the tie bars in the direction of moldclosing, and when the relative moving speed between the movable dieplate and the tie bars reach within the predetermined value, theengaging means operates to engage the tie bars with the movable dieplate mechanically, then after contact of the movable mold with thefixed mold the second drive means operates to press the movable mold tothe fixed mold.

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The above and other objects, features, and advantages of thepresent invention will be made more apparent from the description ofpreferred embodiments with reference to the accompanying drawingswherein:

[0052]FIG. 1 is an outlined sectional view of the mold clampingmechanism of the present invention.

[0053]FIG. 2 is a control block diagram of a controller for the moldclamping mechanism shown in FIG. 1.

[0054]FIG. 3 is a flow chart for explaining the control program for moldclamping operation.

[0055]FIG. 4 is a chart showing speed diagrams of the movable die plate,the tie bars and the half nut.

[0056]FIG. 5 is another mold clamping mechanism of the presentinvention.

[0057]FIG. 6 is an outlined sectional view of the mold clampingmechanism with a pair of molds opened of the prior art.

[0058]FIG. 7 is an outlined sectional view of the mold clampingmechanism with the molds closed corresponding to completion of adjustingmold thickness in FIG. 6.

[0059]FIG. 8 is an enlarged sectional view of the portion of the moldclamping cylinder in FIG. 6.

[0060]FIG. 9 is a chart showing position diagrams of the movable dieplate, the tie bars and the half nut during mold close operation in FIG.6.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0061] The preferred embodiments will be explained below with referenceto FIGS. 1 to 5 of the accompanying drawings.

[0062]FIG. 1 shows an outlined sectional view of main portions of themold clamping mechanism in the injection molding machine.

[0063] In FIG. 1, a reference numeral 50 represents a fix die plate onthe left side of which a fixed mold 52 is fixedly mounted. On the otherhand, against the fixed die plate 50 there is provided with a movabledie plate 56 on the right side of which a moving mold 54 is fixedlymounted.

[0064] A reference numeral 68 represents a tie bar. The right endportion of the tie bar 68 is supported on the fixed die plate 50, andthe left end portion is slidably inserted in the movable die plate 56.

[0065] Incidentally, the injection molding machine usually provides withfour tie bars 68, each being located at the comers of the fixed dieplate 50 and the movable die plate 56.

[0066] Since the each tie bar 68 functions in the same way from thepoint of the subject matter of the present invention, the only one tiebars 68 is illustrated in FIG. 1. Furthermore, in FIG. 1 upper portionsof the fixed die plate and the movable die plate 56 are omitted for wantof space.

[0067] A reference numeral 78 represents a feed screw used for the moldopen and close operation in which the movable die plate 56 advances andretracts to the fixed die plate 50. The right end portion of the feedscrew 78 is rotatably supported by a bearing member 81 mounted on thefixed die plate 50 and further connected through a coupling 82 to thedrive axis of an AC (alternative current) servomotor 74 mounted on rightside of the fixed die plate 50. A reference numeral 76 represents arotary encoder.

[0068] The left side portion of the feed screw 78 screws a nut 80mounted on the movable die plate 56. Therefore, the movable die plate 56is slidably guided by the tie bar 68, and is capable of advancing andretracting to the fixed die plate 50. The encoder 76 always detects amoving distance and a moving direction of the movable die plate 56. Thedetected information is given to a mold clamping controller shown inFIG. 2, and utilized for position control of the movable die plate 56.

[0069] A reference numeral 62 represents a mold clamping cylinder formedin the fixed die plate 50, on the right end surface of which a cover 58is mounted. A piston 66 of the mold clamping cylinder 62 is mounted onthe right end portion of the tie bar 68. A detecting rod 64 fordetecting a position is fastened to the piston 66 at the left end andprotrudes through the cover 58 to a tie bar position sensor 60.

[0070] The tie bar position sensor 60 detects a position of the tie bar68 in a way that the detecting rod 64 moves together with the piston 66.There is formed a screw 70 on the circumference of the left portion ofthe tie bar 68, which engages to a pair of half nuts 73 in a knownengaging means 72. The engaging means 72 is mounted on the left side ofthe movable die plate 56. The engaging means 72 and the half nut 73constitute an engaging portion of the present invention. The detail forsupply and discharge of hydraulic pressured oil is omitted here.

[0071] Though the engaging means 72 is illustrated as a hydraulicsystem, it is also possible to arrange the engaging means 72 in a waythat the half nut 73 is advanced or retracted to the screw 70 byutilizing an electric motor.

[0072] In the above, the main portion of the mold clamping mechanism, towhich the present invention is applied, is explained referring toFIG. 1. The point is such that while the movable die plate 56 moves at alow speed in the direction of right in FIG. 1 under the mold closeoperation, the engaging means 72 operates and finishes the engagement,moving the tie bar 68 in the same direction by driving the mold clampingcylinder 62, thereby enabling to omit works for adjusting the moldthickness required at the initial setting, namely, the works done fromthe past that the engaging means 72 executes engaging operation underthe state of once closing the molds 52 and 54.

[0073]FIG. 2 illustrates a control block diagram of a controller for themold clamping mechanism shown in FIG. 1. In FIG. 2, a reference numeral100 represents an operation processing division for controlling moldclamping operations. The operation processing division 100 isconstituted from a central processing unit CPU, a bus BUS connected tothe CPU, a data memory DM and a program memory PM connected to the BUS,and an interface unit iF for sending and receiving signals betweeninput/output devices located outside. The interface unit iF provideswith the functions of A/D converter and D/A converter.

[0074] Reference numerals 60 and 76 represent the tie bar positionsensor and the rotary encoder as explained in FIG. 1, each supplyinginput signals through the interface unit iF to the operation processingdivision 100. On the other hand, the output signals that the operationprocessing division 100 produces are given through the interface unit iFto a control valve 72A for drive control of the engaging means 72 withthe half nut 73, a control valve 62A for drive control of the moldclamping cylinder 62 and a servo-driver 74A for drive control of the ACservomotor 74. In the case, a signal from the rotary encoder 76 to theservo-driver 74A is used for feedback control of the AC servomotor 74.

[0075] There is provided with a memory area 101 in the program memory PMof the operation processing division 100 for storing a control programfor mold clamping operation, that is, a series of instructions given tothe CPU for executing mold clamping operations.

[0076] Further, there is provided with a memory area 102 in the datamemory DM of the operation processing division 100. In the memory area102 there is predeterminedly stored setting values “a” allowable as therelative speed, that is, values of difference between the moving speedsof the movable die plate 56 and the tie bar 68 during the mold closeoperation.

[0077] In the data memory, besides the setting values “a”, there areprovided with memory areas storing various data necessary for drivecontrol of the mold clamping mechanism, such as a real position andspeed of the tie bar 68, a real position and speed of the movable dieplate 56, a moving speed instruction value and a speed change positionor time to a low speed for the movable die plate 56, a starting positionor time and speed for moving the tie bar 68, and a time for theengagement completion by the engaging means 72. The details are omittedhere.

[0078]FIG. 3 illustrates a flow chart for explaining the control programfor mold clamping operation stored in the memory area 101 in the programmemory PM.

[0079]FIG. 4 illustrates a chart showing speed diagrams of the movabledie plate 56, the tie bar 68 and the half nut 73 in the engaging means72 during the mold close operation, respectively. The process of themold clamping operation is explained below in accordance with each stepin the flow chart of FIG. 3, referring to FIGS. 1, 2 and 4.

[0080] Abbreviated letters MD and TB for the movable die plate and thetie bar are respectively used in the flow chart, because of conveniencefor description.

[0081] The control program for mold clamping operation is initiated inresponse to an instruction of mold close operation given from acontroller (not shown) of the injection molding machine.(START)

[0082] At step ST1, it is instructed that the movable die plate 56advances, that is, moves against the fixed die plate 50 at a high speedset predetermindly. Then, at step ST2, it is judged whether or not themovable die plate 56 reaches a position to change to a low speed. (Theposition corresponds to the time “t1” in FIG. 4)

[0083] In case that the judgment at the step ST2 is negative(hereinafter merely described as “N”), the high speed is still held.Also, in case that the judgment at the step ST2 is positive (hereinaftermerely described as “Y”), it is instructed at step ST3 that the movabledie plate 56 moves at the low speed.

[0084] Then, at step ST4, it is instructed that the tie bar 68 moves ata low moving speed under the condition that the position or time tostart the moving operation of the tie bar 68 is the same with the time“t1” corresponding to the speed change position of the movable die plate56. (a drive instruction to the control valve 62A for mold clampingcylinder 62)

[0085] Further, at step ST5, it is instructed to calculate differencesbetween the moving speeds of the movable die plate 56 and the tie bar68, that is, relative speed from the real moving speeds of them. Therespective real moving speed is given by differentiating the positionsignals from the tie bar position sensor 60 and the encoder 76 in FIG.2.

[0086] At step ST6, it is judged whether or not the relative speed areless than the set values “a” stored in the memory area 102 of the datamemory DM. In case of the judgment “N” at step ST6, it is instructed torepeat steps ST3 to ST6. In case of the judgment “Y” at step ST6, it isinstructed at step ST7 that the half nut 73 advances against the screwportion 70 of the tie bar 68. (a drive instruction to the control valve72A for the nut with divided portions in FIG. 2)

[0087] In the case, a command moving speed to the tie bar 68 is defined,as shown in FIG. 4 as S2, in such a way that difference between thecommand speed and the command low moving speed S1 to the movable dieplate 56 is less than the setting values “a”.

[0088] Further, it is judged at step ST8 whether or not an engagement iscompleted. In case of the judgment “N”, it is instructed at step ST9 towait for a time interval “T1” and then repeat step ST8.

[0089] Also, in case of the judgment “Y” (corresponding to a time “t3”as shown in FIG. 4), it is instructed at step ST10 whether or not themovable die plate 56 reaches the mold close position. In case of thejudgment “N”, it is instructed at step ST11 to wait for a time interval“T2” and then repeat step ST10. Also, in case of the judgment “Y”(corresponding to a time “t4” as shown in FIG. 4), it is instructed atstep ST12 to stop moving of the movable die plate 56 and the tie bar 68.

[0090] Then, it is instructed at step ST13 to supply hydraulic pressuredoil to the chamber located at the left side of the mold clampingcylinder 62 so as to execute the mold clamping operation. Further, it isjudged at step ST14 whether or not the mold clamping operation iscompleted. In case of the judgment “N” it is instructed at step ST15 towait for a time interval “T3” and then repeat step ST14. Also, in caseof the judgment “Y” at step ST14 it is instructed to inform thecompletion of mold clamping operation to the controller.

[0091] Furthermore, though not shown in the flowchart, it is instructedthat the tie bar 68 is forced to move together with the movable dieplate 56 at the low moving speed after the time “t3” corresponding tothe engagement completion judged at step ST8. Accordingly, as shown inFIG. 4, the speed S2 of the tie bar 68 is adjusted to S1 after the time“t3”. In this case, it is also instructed that the control valve 62Aadjusts supplying and discharging of hydraulic pressured oil to the moldclamping cylinder 62 so that the tie bar 68 does not disturb themovement of the movable die plate 56 at the low moving speed.

[0092] Further, in the explanation of the flowchart mentioned above, itis assumed, as shown in FIG. 4, that the time to start the movingoperation of the tie bar 68 is the same with the time “t1” correspondingto the moving speed change from high to low of the movable die plate 56.However, the time to start the moving operation of the tie bar 68 can bedelayed.

[0093] In FIG. 4, the time interval (=t3−t2) corresponds to a timepassage between the start of moving and the completion of engagementwith regard to the half nut 73. The time interval varies in accordancewith the relative speed between the movable die plate 56 and the tie bar68, and a phase shift condition at the time “t2” between the half nut 73and the screw portion 70 of the tie bar 68.

[0094] Accordingly, it is possible to shorten the time interval bychanging the moving speed of the movable die plate 56 or the tie bar 68within the allowance “a” while monitoring the time interval.

[0095] Further, in case that the phase shift is nearly equal to onepitch at monitoring the first mold clamping operation, it is possible tomodify the control program for the next mold clamping operation so as todelay the time to start the tie bar 68 by an appropriate time interval,taking into account of the difference between the moving speeds anddegrees of the phase shift.

[0096]FIG. 5 shows another mold clamping mechanism to which the presentinvention is applied.

[0097] In FIG. 5, reference numerals 50, 52, 54 and 68 represent thesame elements with those in FIG. 1, respectively.

[0098] There are two main different points on structures between FIG. 1and FIG. 5. The one is, as shown in FIG. 5, locating the mold clampingcylinder on the movable die plate side, not on the fixed die plate side.The other is locating a nut 88 in the fixed die plate 50 for moving thetie bar 68 during mold close operation, which is screwed with a screwportion 68A formed on the circumference of right end portion of the tiebar 68, and allowed to rotate but refrained from moving in the directionof axis thereof. The nut 88 is rotated by a servomotor 90 provided witha rotary encoder 91 through a transmitting gear 89 and a gear formed onthe circumference of the nut 88. The tie bar 68 is refrained fromrotating by means of keys, as in FIG. 1.

[0099] In FIG. 5, the movable die plate is provided with two parts, thatis, a first supporting member 56A and a second supporting member 56B.The first supporting member 56A mounts the movable mold 54 on one sideand a ram 86 on the opposite side fixedly.

[0100] The second supporting member 56B is provided with a mold clampingcylinder 95 formed therein. The other end portion of the ram 86 isformed with its diameter bigger and slidably inserted as a piston in thecylinder 95. The tie bar 68 is slidably inserted both on the firstsupporting member 56A and the second supporting member 56B.

[0101] Reference numerals 92 and 94 represent a nut with dividedportions and a hydraulic cylinder for driving, respectively, by whichthe screw portion 68B is engaged, as the engaging means 72 in FIG. 1.

[0102] A reference numeral 84 represents a hydraulic cylinder for moldclose operation. The end portion of the piston rod of the cylinder 84 isfixed to a support member 56C mounted on the lowest portion of the firstsupporting member 56A.

[0103] In the mold clamping mechanism shown in FIG. 1, the mold clampingcylinder 62 executes both functions of moving the tie bar 68 during themold close operation and of the essential mold clamping operation afterthe mold close operation. However, in FIG. 5 the mold clamping cylinder95 has not such combined functions. Though not illustrated, somemodifications to the embodiments described above are possible.

[0104] The one is to apply the mold clamping mechanism shown in FIG. 1to a die casting machine.

[0105] Another one is to constitute the nut for the engaging means withportions divided more than three.

[0106] Still another one is to constitute a drive means for advance andretract of the nut with divided portions by means of a servomotor withposition detectors.

[0107] Still another one is to constitute the circumference of the tiebar as an engaging portion to be with rack like formation.

[0108] Other one is to constitute a groove width of the screw or rackportion on the tie bar to be bigger than that of the screw thread on thenut, or to constitute the groove having a slope for easily engaging.

[0109] Such a modification is considered as alteration of design, ordesign around on the present invention.

[0110] According to the method for mold clamping of the presentinvention, there is an advantage that it executes mold clampingoperation without any initial setting works for adjusting thickness ofmolds and enables the engaging means to operate for completion ofengagement making use of the difference of moving speed between themovable die plate and the tie bars during mold close operation, and asthe result it greatly shorten the molding cycle, since it executes amold clamping operation in such a way that, while the mold closeoperation in which the first drive means moves the movable die plate tothe fixed die plate, the third drive means moves the tie bars in thedirection of mold closing, and when the relative moving speed betweenthe movable die plate and the tie bars reaches within the predeterminedvalue, the engaging means operates to engage the tie bars with themovable die plate mechanically, then after contact of the movable moldwith the fixed mold the second drive means operates to press the movablemold to the fixed mold.

[0111] Furthermore, according to the apparatus for mold clamping of thepresent invention, there is another advantage, in addition to theadvantage mentioned above, that it executes automatically the moldclamping operation by the present invention, since it is provided with amold clamping mechanism comprising a fixed die plate fixedly mounting afixed mold thereon, a movable die plate fixedly mounting a movable moldthereon and facing to the fixed die plate, a tie bars supported at oneend portion by the fixed die plate and slidably supporting the movabledie plate so as to advance and retract to the fixed die plate, a firstdrive means for executing mold open and close operations by advancingand retracting the movable die plate to the fixed die plate, a seconddrive means for executing mold clamping operation by pressing themovable die plate against the fixed die plate after the movable moldcontacts with the fixed mold by operating the first drive means, a thirddrive means for executing relative movement between the tie bars and themovable die plate in the direction of axes of the tie bars and anengaging means mounted on the movable die plate for executing anengagement with a engaging portion formed on circumference of the tiebars, and further a mold clamping controller for drive control of thefirst drive means, the second drive means, the third drive means and theengaging means,

[0112] the mold clamping controller constituting

[0113] a first command division for instructing a low moving speed ofthe movable die plate to the first drive means during mold closeoperation, and for instructing a moving speed of the tie bars differentfrom the low moving speed to the third drive means at the same time whenthe low moving speed is instructed or thereafter,

[0114] a detector for detecting a relative moving speed between themovable die plate and the tie bars,

[0115] a setting division for setting a preferable relative movingspeed, within which the engaging means is capable of engagement, and

[0116] a second command division for instructing the engaging operationwhen an output signal of the detector reaches the preferable relativemoving speed.

[0117] Furthermore, according to the apparatus for mold clamping of thepresent invention, there is still another advantage, in addition to theforegoing advantage, that the structure of the mechanism is constitutedwith much simpler than before, since the second drive means is used asthe third drive means utilizing that each the second and the third drivemeans operates at different time zone.

[0118] It should be understood, of course, that the foregoing disclosurerelates only to preferred embodiments of the invention, and that it isintended to cover all changes and modifications of the example of theinvention herein chosen for the purpose of the disclosure which does notconstitute departures from the spirit and scope of the invention setforth in the appended claims.

What is claimed is:
 1. Method for mold clamping in an injection moldingmachine and the like having a mold clamping mechanism comprising a fixeddie plate fixedly mounting a fixed mold thereon, a movable die platefixedly mounting a movable mold thereon and facing to said fixed dieplate, tie bars supported at one end portion by said fixed die plate andslidably supporting said movable die plate so as to advance and retractto said fixed die plate, a first drive means for executing mold open andclose operations by advancing and retracting said movable die plate tosaid fixed die plate, a second drive means for executing mold clampingoperation by pressing said movable die plate against said fixed dieplate after said movable mold contacts with said fixed mold by operatingsaid first drive means, a third drive means for executing relativemovement between said tie bars and said movable die plate in thedirection of axes of the tie bars and an engaging means mounted on saidmovable die plate for executing an engagement with a engaging portionformed on circumference of said tie bars, said method comprising thesteps of starting movement of said tie bar in the direction of moldclosing by said third drive means so that said tie bar moves atdifferent moving speed with that of said movable die plate during moldclose operation in which said movable die plate moves against said fixeddie plate by said first drive means, judging a relative moving speedbetween said movable die plate and said tie bars within a predeterminedvalue, engaging said tie bars with said movable die plate mechanicallyby operating said engaging means when the relative moving speed isjudged to be within the value, then driving said second drive means,thereby executing mold clamping operation.
 2. In the method for moldclamping as in claim 1, wherein said starting movement of said tie barsare executed at the same time when the moving speed of said movable dieplate changes from high to low by said first drive means.
 3. In themethod for mold clamping as in claim 1 or 2, wherein either one or bothof the moving speeds of said movable die plate and said tie bar arechanged in case that said engaging operation is still on the way at aprescribed time passage after said engaging means starts to operate. 4.In the method for mold clamping as in claim 1 or 2, wherein a timing forstarting movement of said tie bar is varied at next mold clampingoperation, based on a time interval between start and completion of saidengaging operation.
 5. In an apparatus for mold clamping in an injectionmolding machine and the like having a mold clamping mechanism comprisinga fixed die plate fixedly mounting a fixed mold thereon, a movable dieplate fixedly mounting a movable mold thereon and facing to said fixeddie plate, tie bars supported at one end portion by said fixed die plateand slidably supporting said movable die plate so as to advance andretract to said fixed die plate, a first drive means for executing moldopen and close operations by advancing and retracting said movable dieplate to said fixed die plate, a second drive means for executing moldclamping operation by pressing said movable die plate against said fixeddie plate after said movable mold contacts with said fixed mold byoperating said first drive means, a third drive means for executingrelative movement between said tie bar and said movable die plate in thedirection of axis of the tie bars and an engaging means mounted on saidmovable die plate for executing an engagement with an engaging portionformed on circumference of said tie bars, and further having a moldclamping controller for drive control of said first drive means, saidsecond drive means, said third drive means and said engaging means, saidmold clamping controller comprises a first command division forinstructing a low moving speed of said movable die plate to said firstdrive means during mold close operation, and for instructing a movingspeed of said tie bar different from the low moving speed to said thirddrive means at the same time when said low moving speed is instructed orthereafter, a detector for detecting a relative moving speed betweensaid movable die plate and said tie bars, a setting division for settinga preferable relative moving speed, within which said engaging means iscapable of engagement, and a second command division for instructing theengaging operation when an output signal of the detector reaches thepreferable relative moving speed.
 6. Apparatus for mold clamping as inclaim 5, wherein said second drive means is also used as said thirddrive means.
 7. Apparatus for mold clamping as in claim 6, wherein saidsecond drive means used as said third drive means is provided with amold clamping cylinder located at a portion of the fixed die plate onwhich said tie bars are supported, and one end of said tie bars beingformed as a piston slidably located in said clamping cylinder. 8.Apparatus for mold clamping as in claim 5, wherein said second drivemeans is provided with a mold clamping cylinders located in said movabledie plate, and said third drive means is provided with a screw portionformed on circumference of said tie bars which locates at a supportingportion in said fixed die plate, a nut located in said fixed die plate,which is screwed with said screw portion and refrained from moving inthe direction of axis and a drive motor for rotating said nut. 9.Apparatus for mold clamping as in any one of the claims 5 to 8, whereinsaid first drive means is provided with an electric servomotor mountedon said fixed die plate, screw axes connected with rotating axis of saidservomotors and extending to said movable die plate and nuts mounted onsaid movable die plate and screwed with said screw axis.
 10. Apparatusfor mold clamping as in claims 5, wherein said engaging means isprovided with a pair of half nuts and a driving means for advancing andretracting them to an engaging portion.
 11. Apparatus for mold clampingas in claims 10, wherein said engaging means is provided with aplurality of half nuts.